The purpose of this work is to clarify the mechanism of cell transformation by examining the genetic and physiological factors which affect cell transformation induced by chemicals and irradiation. Comparative studies of the susceptibilities to transformation and mutation induction between cell variants and the effects of growth condition after ultraviolet (UV) radiation on the fixation and expression of transformation and mutation induction suggest the existence of a difference in the process or induction between transformation and mutation although there are similarities between the two processes.